Portland pitcher Mike Shawaryn delivers in the second inning against Harrisburg in Portland on Tuesday. (Derek Davis/Portland Press Herald Photo)

PORTLAND — This so-called depleted Red Sox farm system is producing fine pitching at the Double-A level these days.

The Portland Sea Dogs got another superb start and backed it with relievers on a roll. The result was a 1-0 win over the Harrisburg Senators on Tuesday night, before 4,847 at Hadlock Field.

Portland’s run came on back-to-back doubles in the first inning by Danny Mars and Michael Chavis.

Starter Mike Shawaryn (6-7) and the bullpen made it hold up. The Senators didn’t get a runner beyond second base.

Shawaryn pitched seven innings, allowing five hits and two walks, striking out four. He mixed a 91-93 mph fastball with his cutter and improved change-up, throwing 88 pitches (56 strikes).

“Mike’s doing a lot of things well,” pitching coach Paul Abbott said. “He’s pitching with a lot of confidence, for one. His change-up has really improved with late movement, which he didn’t have earlier in the year — to go with a plus-fastball and a plus cutter. And he’s throwing inside more. He’s on a good run.”

Shawaryn, Boston’s No. 9 prospect (ranked by milb.com), lowered his ERA to a rotation-leading 3.29. Of his 18 starts, 12 have featured two earned runs or less. And the change-up gives him a third threat.

“It’s coming along,” Shawaryn said. “Now we’re in the final stage of me trusting it more to throw in games.”

In the past eight games, Sea Dogs starters have allowed a total of two earned runs. Portland (42-58) is 6-2 in those games, with five shutouts.

“We’ve had a really good stretch,” Shawaryn said. “We have a good plan of attack and we’re utilizing the (scouting reports), and I believe we’re getting better every day.”

Travis Lakins (0.90 ERA as a reliever) pitched a scoreless eighth and Trevor Kelley (3.90) got the ninth for his five save.

The Senators outhit the Sea Dogs 7-5 but Portland got the two key hits.

With one out in the first, Mars hit a hard grounder that bounced off first base. As it rolled into right field, he hustled to second. Chavis, who hadn’t played in 10 days because of a sore wrist, then got an outside slider from Jaron Long (3-7) and crushed a line drive into the right-center gap, easily scoring Mars.

Harrisburg dropped to 51-50.

NOTES: The Sea Dogs’ batting practice featured an extra player with pitcher Trey Ball taking swings. Before the Red Sox drafted Ball seventh overall in 2013, some teams considered him more valuable as a hitter. Ball, 24, who has struggled on the mound, began taking batting practice “about a month ago,” Sea Dogs Manager Darren Fenster said. “He had a pretty impressive track record as a position player and we thought ‘let’s see what we’ve got.’ He’s not going into games anytime soon.” Ball went on the disabled list Sunday (undisclosed reasons). He has a 7.23 ERA in 25 relief appearances. Ball said he was “trying something new. I’ve hit some rough patches on the mound and just trying to keep my mind off that.”

Michael Chavis of Portland prepares to bat in the third inning against Harrisburg in Portland on Tuesday. (Derek Davis/Portland Press Herald Photo)

Jeremy Rivera of Portland steals second base as Carter Kieboom of Harrisburg takes the throw in the third inning in Portland on Tuesday. (Derek Davis/Portland Press Herald Photo)

Jeremy Rivera of Portland throws to first for a double play after forcing out Dan Gamache of Harrisburg in the fourth inning in Portland on Tuesday. (Derek Davis/Portland Press Herald Photo)